The invention relates generally to semiconductor device fabrication and, in particular, to device structures for a bipolar junction transistor, as well as fabrication methods and design structures for a bipolar junction transistor.
Bipolar junction transistors are multi-terminal electronic devices that include three main terminal regions defining an emitter, an intrinsic base, and a collector. Bipolar junction transistors come in two types or polarities, known as PNP and NPN based on the doping types of the three main terminal regions. An NPN bipolar junction transistor includes two regions of n-type semiconductor material constituting the emitter and collector, and a thin region of p-type semiconductor material sandwiched between the two regions of n-type semiconductor material to constitute the intrinsic base. A PNP bipolar junction transistor includes two regions of p-type semiconductor material constituting the emitter and collector, and a thin region of n-type semiconductor material sandwiched between the two regions of p-type semiconductor material to constitute the base. The differing doping types of the emitter, base, and collector define a pair of p-n junctions, namely a collector-base junction and an emitter-base junction, across which the conductivity type changes. In use, a voltage applied across the emitter-base junction controls the movement of charge carriers to produce charge flow between the collector and emitter.
Bipolar junction transistors may be found, among other end uses, in high-frequency and high-power applications. The heterojunction bipolar transistor is a type of bipolar junction transistor that uses differing semiconductor materials for the emitter and base regions, which creates a heterojunction. Heterojunction bipolar transistors may find particular use in radiofrequency integrated circuits, which are used in wireless communications systems, power amplifiers in mobile devices, etc.
Improved device structures, fabrication methods, and design structures are needed for bipolar junction transistors.